Hybrid inflator and related propellants

ABSTRACT

A hybrid inflator for an automotive inflatable safety system is disclosed. In one embodiment, a mixture of an inert gas (e.g., argon) and oxygen are contained within the inflator housing and a hybrid propellant (i.e., ballistic properties similar to double-base and long-term stability similar to LOVA) is included in the gas generator.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent. applicationSer. No. 08/210,668, entitled "Hybrid Inflator", and filed Mar. 18,1994.

FIELD OF THE INVENTION

The present invention generally relates to the field of automotiveinflatable safety systems and, more particularly, to hybrid inflatorswhich utilize both a stored, pressurized gas and a gas and/or heatgenerating propellant.

BACKGROUND OF THE INVENTION

The evolution of inflators for automotive inflatable safety systems hasresulted in the development of pressurized gas only inflators,propellant only inflators, and hybrid inflators. Hybrid inflatorsutilize a combination of a stored, pressurized gas and gas and/or heatgenerating propellant to expand the air/safety bag. There are of coursemany design considerations for each of these types of inflators. In allthree systems, two primary design considerations are that the air/safetybag must be expanded a predetermined amount in a predetermined amount oftime in order to be operationally effective. Moreover, since the gaswithin the expanded air/safety bag eventually permeates through theair/safety bag and is discharged to atmosphere, the effect of the gasesupon occupants of the automobile is important.

With further regard to the effect of the gases upon the occupants, forinstance it is desirable to have the gases within the air/safety bag bebelow a certain toxicity level. U.S. Pat. Nos. 3,690,695; 3,788,667; and3,966,226 generally address this issue. Moreover, the appearance of thegases is important. As an example, one problem with currentstate-of-the-art hybrid inflators is that they produce, in the gasoutput stream, copious quantities of metal salt fumes (e.g., potassiumchloride). This salt is present because an oxygen source has been addedto the propellant formulation to minimize carbon monoxide production byoxidizing all carbon in the propellant to carbon dioxide. This salt fumeis highly objectional in a crash situation because it has bothphysiological and psychological effects, imposed at a time of greatphysical and psychological stress. The salt fume in the post-crashautomobile cabin drastically reduces visibility for the crash victims,and creates anxiety over the possibility of fire. Current hybridinflators use propellants which typically contain more than 70%potassium perchlorate, which yields about 54% of the propellant weightas potassium chloride fume.

Since the weight of the automobile is an important design considerationin many instances today, so too then is the weight of the inflator.Moreover, due to the limited space available in many automotive designs,the size of the inflator is also an important design consideration.These types of factors have effectively rendered pressurized gas onlyinflators obsolete. Moreover, in propellant only and hybrid inflators,these types of considerations have resulted in many changes to thestructure of the inflator and the materials selected for use in thisstructure. However, little consideration has been given to thepropellant to achieve a certain weight reduction.

Although the performance of a given inflator will of course influencethe manufacturer's/supplier's position in the marketplace, systemperformance alone is no longer dispositive. That is, since inflatablesafety systems are now being included in a large number of automobileswhich will likely increase the number of manufacturers/suppliers ofinflators, minimizing the cost of the inflator is becoming increasinglyimportant to obtaining a competitive advantage. Consequently, it wouldbe desirable to not only provide an inflator with competitiveperformance characteristics, but which is also cost competitive.

SUMMARY OF THE INVENTION

The present invention generally relates to a hybrid inflator for anautomotive inflatable safety system. That is, the invention relates toan inflator which utilizes both a stored, pressurized gas and a gasand/or heat generating propellant to expand the air/safety bag. Morespecifically, the various aspects of the present invention may beembodied in a hybrid inflator which uses a propellant which producesrelatively large amounts of carbon monoxide and hydrogen. This wouldnormally be unacceptable in an inflator for an automotive inflatablesafety system. However, a sufficiently acceptable amount of thesecombustion products are converted to harmless carbon dioxide and watervapor by oxygen which is used as at least part of the stored,pressurized gas of the hybrid inflator. This stored oxygen eliminatesthe need for an oxygen source (e.g., potassium perchlorate) in thepropellant formulation itself, and thereby eliminates the largest sourceof objectionable particulate fume production in the inflator. Thereaction of carbon monoxide and hydrogen produced by the propellant withthe oxygen stored in the inflator as a gas also greatly enhances theheating value of the propellant, thereby minimizing the amount ofpropellant required.

One aspect of the present invention is directed toward a hybrid inflatorwhich utilizes a secondary explosive (e.g., nitramines such as RDX(hexahydrotrinitrotriazine) and HMX (cyclotetramethylenetetranitramine),PETN (pentaerythritol tetranitrate), TAGN (triaminoguanidine nitrate) inthe propellant formulation (which may also include appropriate inert orenergetic binders, inert or energetic plasticizers, and/or stabilizersfor providing an appropriate burn rate, manufacturability, long-termthermal stability (aging properties), and mechanical properties). Sincethese types of propellants generate relatively significant quantities ofcarbon monoxide and hydrogen, it is desirable to utilize two types ofstored gases within the inflator housing. For instance, one of the typesof gases may be an inert gas(es) such as argon and may comprise amajority of the stored gas, while the other type of gas may be oxygen.Argon has advantages such as that it is relatively inexpensive, inert,has a relatively large molecule and thus is relatively easy to store ata high pressure (e.g., 3,000 psi) for an extended period of time, andhas a low heat capacity. Oxygen is advantageous in that it willexothermically react with the propellant gases and reduce toxicity.Moreover, this reaction generates heat which further contributes to theexpansion of the argon by the propellant gases, thereby allowing use ofreduced amounts of propellant. Moreover and as noted, the reactionreduces the toxicity of the propellant gases to acceptable levels bydriving the reaction equilibrium to CO₂ and H₂ O.

Another aspect of the present invention relates to specific propellantformulations which include a secondary explosive and which may be usedin hybrid inflators. Initially, these propellant formulations exhibitballistic properties generally similar to that of double-basepropellants and long-term thermal stability properties generally similarto that of LOVA propellants. Consequently, these propellant formulationsare hereinafter referred to as "hybrid propellants".

The hybrid propellant formulations of the above-noted aspect of thepresent invention include a binder system (preferably energetic) whichmay include a binder, plasticizer, and/or stabilizer (e.g., one or morecompounds which are useful to modify the physical, chemical, and/orballistic properties) in combination with a secondary explosive, andfurther have a burn rate ranging from about 0.1 inches per second (0.25cm/sec) to about 1 inch per second (2.5 cm/sec) at about 4,000 psi (27.6MPa), a combustion temperature ranging from about 2,000° K. to about3,800° K., and exhibit acceptable long-term thermal stability (e.g., oneindustry test is that the inflator will perform acceptably afterexposure to 100° C. for a period of 400 hours).

The binder system included with the secondary explosive in the notedhybrid propellant formulation as noted may include a binder, preferablyone which is easily combustible at the above-noted combustiontemperatures and pressures (e.g., cellulose acetate, GAP (a glycidylazide polymer which burns significantly more vigorously than celluloseacetate). Moreover, the binder system as noted may also include aplasticizer, preferably one which is "energetic" versus inert (e.g.,nitrate ester plasticizers such as TMETN (trimethylolethane trinitrate)or TEGDN (triethyleneglycol dinitrate), or azide substituted polymerssuch as a GAP plasticizer (e.g., a monomer of the noted glycidyl azidepolymer)). Furthermore, and as noted, for certain plasticizers it may befurther desirable to also utilize a "stabilizer" in the hybridpropellant formulation, namely a material which will "retard" thermaldecomposition of the binder and/or plasticizer to a degree up to acertain temperature such that the potential for autoignition at or belowthis temperature is reduced. That is, stabilizers may be used forachieving acceptable long-term thermal stability for hybrid propellantformulations which use a binder and/or plasticizer which, if notstabilized, would render the long-term thermal stability of the hybridpropellant formulation generally unacceptable.

One specific hybrid propellant formulation based upon the secondaryexplosive and binder system which may be used in a hybrid inflatorincludes RDX (hexahydrotrinitrotriazine), cellulose acetate (binder),TMETN (trimethylolethane trinitrate) (an energetic nitrate esterplasticizer) and ethyl centralite (stabilizer). Another hybridpropellant formulation based upon the secondary explosive and bindersystem which may be used in a hybrid inflator includes RDX(hexahydrotrinitrotriazine), GAP (glycidyl azide polymer) (binder), andan appropriate plasticizer (e.g., a GAP monomer, TMETN). In order toreduce the cost of this formulation, cellulose acetate may be used incombination with the GAP as the binder, and ATEC (acetyl triethylcitrate and a plasticizer) may also be used in combination with the GAPmonomer plasticizer.

Another aspect of the present invention relates to a hybrid inflatorhaving a modified gas generator structure, for instance to accommodatefor use of the above-described propellants. Generally, the inflatorincludes an inflator housing with a pressurized medium therein. The gasgenerator is interconnected with the inflator housing and includes a gasgenerator housing which contains a propellant. The sidewall of the gasgenerator housing has at least one and preferably a plurality of gasgenerator outlets, and at least one gas generator inlet is positioned onan end of the gas generator housing. When the inflator is activated suchthat the pressurized medium begins flowing by the sidewall of the gasgenerator housing and out of the inflator, a pressure differentialdevelops such that pressurized medium is drawn into the gas generatorhousing through the gas generator inlet. Consequently, it will beappreciated that this is advantageous for mixing the above-describedpressurized medium, and particularly the oxygen portion thereof, withthe combustion products of the above-noted types of propellant.Nonetheless, gases are discharged through the gas generator outlet(s) onthe sidewall of the gas generator housing to augment the discharge fromthe inflator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an automotive inflatable safetysystem;

FIG. 2 is a longitudinal cross-sectional view of a hybrid inflator whichmay incorporate one or more principles of the present invention;

FIG. 3 is an inflator internal pressure versus time performance curvefor the propellant composition of Example 2; and

FIG. 4 is a receiving tank pressure versus time performance curve forthe propellant composition of Example 2.

DETAILED DESCRIPTION

The present invention will be described with regard to the accompanyingdrawings which assist in illustrating various features of the invention.In this regard, the present invention generally relates to hybridinflators for automotive inflatable safety systems. That is, theinvention relates to an inflator which utilizes both a stored,pressurized gas and a gas and/or heat generating propellant. Varioustypes of hybrid inflators are disclosed in U.S. Pat. No. 5,230,531 toHamilton et al. which is assigned to the assignee of this application,and the entire disclosure of this patent is hereby incorporated byreference in its entirety herein.

One embodiment of an automotive inflatable safety system is generallyillustrated in FIG. 1. The primary components of the inflatable safetysystem 10 include a detector 14, an inflator 26, and an air/safety bag18. When the detector 14 senses a condition requiring expansion of theair/safety bag 18 (e.g, a predetermined deceleration), a signal is sentto the inflator 26 to release gases or other suitable fluids from theinflator 26 to the air/safety bag 18 via the conduit 22.

The inflator 30 illustrated in FIGS. 2 is a hybrid inflator and may beused in the inflatable safety system 10 of FIG. 1 in place of theinflator 26. Consequently, the inflator 30 includes a bottle or inflatorhousing 34 having a pressurized medium 36 that is provided to theair/safety bag 18 (FIG. 1) at the appropriate time, as well as a gasgenerator 82 that provides propellant gases to augment the flow to theair/safety bag 18 (e.g., by providing heat to expand the pressurizedmedium 36 and/or generating additional gases). As will be discussed inmore detail below, a gun-type propellant (e.g., a high temperature,fuel-rich propellant) may be used for the formulation of the propellantgrains 90 positioned in the gas generator 82 and a mixture of at leastone inert gas (e.g., argon) and oxygen may be used for the pressurizedmedium 36.

The inflator housing 34 and gas generator 82 are interconnected, withthe gas generator 82 being positioned inside the inflator housing 34 toreduce the space required for the inflator 30. More specifically, ahollow diffuser 38 is welded to one end of a hollow boss 66 (e.g.,having a diameter of about 1.25"). The diffuser 38 has a plurality ofrows of discharge holes 40 (e.g., 80 discharge holes 40 each having adiameter of about 0.100") therethrough which provides a "non-thrustingoutput" from the inflator 30 and a screen 58 is positioned adjacent thedischarge holes 40. A closure disk 70 is appropriately positioned withinthe boss 66 and is welded thereto in order to initially retain thepressurized medium 36 within the inflator housing 34. When release isdesired, a projectile 50 having a substantially conically-shaped head ispropelled through the closure disk 70. More particularly, the projectile50 is positioned on the convex side of the closure disk 70 within abarrel 54 and is propelled by the activation of an initiator 46 when anappropriate signal is received from the detector 14 of the inflatablesafety system 10 (FIG. 1). A ring 62 is provided to initially retain theprojectile 50 in position prior to firing.

An orifice sleeve 74 is welded to the closure disk 70 and/or the end ofthe boss 66. The orifice sleeve 74 is hollow and includes a plurality oforifice ports 78 (e.g., four ports 78 each having a diameter of about0.201") to fluidly interconnect the interior of the inflator housing 34and the interior of the boss 66 and diffuser 38 when the closure disk 70is ruptured by the projectile 50. Moreover, the gas generator 82, morespecifically the gas generator housing 86, is welded to the orificesleeve 74 to complete the interconnection of the inflator housing 34 andgas generator 82.

The gas generator housing 86 contains a plurality of propellant grains90 which when ignited provide heated propellant combustion product gasesfor augmenting the flow to the air/safety bag 18 (FIG. 1). Thepropellant grains 90 are retained within the gas generator housing 86 bya propellant sleeve 94 which is separated from the gas generator inletnozzle 98 on the end 96 of the gas generator housing 86 by a screen 104and baffle 100. As will be discussed below, the propellant grains 90 maybe formulated from a gun-type propellant. Nonetheless, the grains 90 aresubstantially cylindrically-shaped with a single hole extending throughthe central portion thereof. Other propellant grain configurations maybe appropriate and will depend at least in part on the particularpropellant formulation being used.

A single (or multiple) gas generator inlet nozzle 98 (e.g., a singlenozzle 98 having a diameter of about 0.516") is positioned on the end 96of the gas generator housing 86 and is generally directed away from theclosure disk 70. The gas generator housing 86 also includes a pluralityof circumferentially spaced outlet or discharge nozzles 200 (e.g., one"row" of four nozzles 200 each having a diameter of about 0.221") on thesidewall of the housing 86. It may be desirable to vary the axiallocation of these nozzles 200 (they may be generally at the mid-portionof the housing 86), although operations may be enhanced by a locationmore proximate the outlet. Moreover, it may be desirable to vary thenumber of nozzles 200. With this configuration of having dischargenozzles 200 on the sidewall of the gas generator housing 86 and an inletnozzle 98 on the end 96 of the housing 86, during combustion of thepropellant grains 90 the pressurized medium 36 is drawn into the gasgenerator housing 86 through the inlet nozzle 98 and the mixed gasesfrom within the gas generator housing 86 flow out of the housing 86through the nozzles 200. Specifically, the flow of pressurized medium 36by the sidewall of the gas generator housing 86 produces a pressuredifferential which draws pressurized medium 36 into the gas generatorhousing 86 through the inlet nozzle 98. This significantly improves uponthe performance of the inflator 30 at least when certain typespropellant gases are produced as will be discussed in more detail below.

The gas generator 82 includes an ignition assembly 114 for igniting thepropellant grains 90 at the appropriate time. The ignition assembly 114is at least partially positioned within the gas generator housing 86between the projectile 50 and propellant grains 90 and generallyincludes an actuation piston 124, and at least one percussion primer 120and an ignition/booster material 144 which serve as an activator. Moreparticularly, an actuation guide 140 engages an end portion of theorifice sleeve 74 and the interior wall of the gas generator housing 86,the actuation guide 140 thereby functioning at least in part to containat least a portion of and guide the actuation piston 124 positionedtherein. A primer holder 116 engages an end of the actuation guide 140and houses a plurality of conventional percussion primers 120 which arepositioned substantially adjacent to the ignition/booster material 144.The ignition/booster material 144 is typically retained adjacent theprimers 120 by a charge cup 148. An example of an appropriateignition/booster material 144 is an RDX aluminum booster material havinga composition of 89% RDX, 11% aluminum powder, with 0.5%hydroxypropylcellulose added. A retainer 108 and baffle 112 arepositioned between the primer holder 116 and propellant sleeve 94. Inthe event that the gas generator housing 86 is attached to the orificesleeve 74 by crimping instead of welding, the gas generator housing 86may have a tendency to lengthen during operation. Consequently, in orderto maintain a firm interaction of the foregoing components, a wavespring washer (not shown) may be positioned, for instance, between theretainer 108 and the baffle 112.

The actuation piston 124 is slidably positioned within the actuationguide 140 and includes a continuous rim projecting member 128 which issubstantially aligned with the primers 120. As can be appreciated, aplurality of projecting members (not shown), could replace thesubstantially continuous rim projecting member 128. A belleville washer136 is positioned between and engages a portion of both the actuationguide 140 and actuation piston 124 (via a spacer 126) to initiallymaintain the position of the actuation piston 124 away from the primers120. Consequently, the potential for inadvertent engagement of theactuation piston 124 with the primers 120, which could activate the gasgenerator 82, is reduced. However, after the projectile 50 passesthrough the closure disk 70, the energy transferred to the actuationpiston 124 by the projectile 50 is sufficient to overcome the bellevillewasher 136 such that the projecting rim 128 is able to engage theprimers 120 with sufficient force to ignite at least one of such primers120. This in turn causes ignition of the ignition/booster material 144,and thus ignition of the propellant grains 90 results.

During operation of the gas generator 82, the primers 120 may erode andthereby allow propellant gases generated by combustion of the propellantgrains 90 to flow through the primers 120. Any leakage of propellantgases in this manner may adversely affect the consistency of performanceof the inflator 30. These gases, however, desirably act upon theactuation piston 124 to move the piston 124 into sealing engagement withthe actuation guide 140. This provides a seal for the gas generatorhousing 90 which substantially limits any leakage of gases therethrough.Therefore, the propellant gases desirably flow through the gas generatornozzle 98.

Summarizing the operation of the inflator 30, the detector 14 (FIG. 1)sends a signal to the initiator 46 to propel the projectile 50. Theprojectile 50 initially passes through the closure disk 70 to open thepassageway between the inflator housing 34 and air/safety bag 18 (FIG.1). The projectile 50 continues to advance until it impacts theactuation piston 124 which causes the projecting rim 128 attachedthereto to strike at least one of the aligned primers 120. As a result,the ignition/booster charge 144 ignites, which in turn ignites thepropellant grain 90. During combustion of the grains 90 within thehousing 86, the pressurized medium 36 from the inflator housing 34 isdrawn into the gas generator housing 86 through the inlet nozzle 98positioned on the end 96 of the housing 86. This results from the flowof the pressurized medium 36 by the sidewall of the gas generatorhousing 86 which produces a pressure differential. This "drawing in" ofthe pressurized medium 36 promotes mixing of the propellant gases andthe pressurized medium 36 within the housing 86, and as will bediscussed in more detail below this is particularly desirable whenoxygen is included in the pressurized medium 36 to react with propellantgases having a large content of carbon monoxide and hydrogen.Nonetheless, gases are discharged from gas generator housing 86 throughthe discharge nozzles 200 on the sidewall of the housing 86. As such,the flow to the air/safety bag 18 is desirably augmented (FIG. 1) bymixing of the pressurized medium 36 with the combustion products fromthe gas generator housing 86.

As noted above, the hybrid inflator 30 may utilize a gun-typepropellant, as the formulation for the propellant grains 90, and amixture of at least one inert gas and oxygen for the pressurized medium36. Gun-type propellants, as used herein, are high temperature,fuel-rich propellants such as single, double, or triple-basepropellants, and nitramine propellants such as LOVA or HELOVApropellants. More specifically, traditional gun-type propellants arethose having a combustion temperature ranging from about 2,500° K. toabout 3,800° K., and typically greater than about 3,000° K., and arefuel-rich in that without excess oxygen, these propellant generatesignificant amounts of CO and H₂. The excess of fuel from thesepropellants typically requires additional oxygen between 5 and 25 molepercent, or sometimes even between 15 and 40 mole percent, of the storedgas to drive the reaction equilibrium to CO₂ and H₂ O.

Specific "traditional" gun-type propellants which may be used for thepropellant grains 90 of the hybrid inflator 30 include HPC-96, a doublebase, smokeless propellant having a composition, on a weight percentagebasis, of about 76.6% nitrocellulose of which about 13.25% is nitrogen;about 20.0% nitroglycerin; about 0.6% ethyl centralite; about 1.5%barium nitrate; about 0.9% potassium nitrate; and about 0.4% graphite.HPC-96 is available from Hercules, Inc. in Wilmington, Del. Since thisparticular double-base propellant includes nitrocellulose as a majoringredient, it cannot meet current auto industry standards for long-termthermal stability, although it does produce desirable ballisticoperation.

LOVA propellants (low vulnerability ammunition) and HELOVA propellants(high energy, low vulnerability ammunition) are another "traditional"gun-type propellant which may also be used for the propellant grains 90,such as a M39 LOVA propellant having a composition, on a weightpercentage basis, of about 76.0% RDX (hexahydrotrinitrotriazine); about12.0% cellulose acetate butyrate; about 4.0% nitrocellulose (12.6%nitrogen); about 7.60% acetyl triethyl citrate; and about 0.4% ethylcentralite. The M39 LOVA propellant is available from the Naval SurfaceWarfare Center in Indianhead, Md. and Bofors in Europe (Sweden) andgenerates, without excess oxygen, about 32 mole percent CO and 30 molepercent H₂. The LOVA and HELOVA propellants are preferred over existingdouble-base propellants because they pass current U.S. automotiveindustry thermal stability standards, whereas double-base propellants donot. However, relatively high operating pressures are required forstable combustion of LOVA and HELOVA propellants. Notwithstanding thecharacteristics of the HPC-96 and LOVA propellants, they do serve toillustrate at least some of the principles/features of the presentinvention.

Due to the performance characteristics of gun-type propellants when usedas the formulation for the propellant grains 90, together with the useof oxygen as a portion of the pressurized medium 36, it is possible toreduce the amount of propellant required for the gas generator 82compared to current designs using, for example, 20-30 grams of FN1061-10 available from the assignee of this patent application (FN1061-10 has a composition, on a weight percentage basis, of about 7.93%polyvinyl chloride, 7.17% dioctyl adipate, 0.05% carbon black, 0.35%stabilizer, 8.5% sodium oxalate, 75% potassium perchlorate, and about 1%lecithin). For instance, generally for gun-type propellants which may beused in the formulation of the propellant grains 90 the total grainweight may range (in passenger side applications) from about 10 grams toabout 12 grams, and is preferably less than about 15 grams. In thiscase, it is preferable to utilize between about 150 grams and about 190grams of pressurized medium 36 with the oxygen being between about 10%to about 30% of this medium 26 on a molar basis. More specifically, whenabout 169 grams of the pressurized medium 36 is utilized, with about 15%of this on a mole percentage basis being oxygen, the total weight of thepropellant grains 90 may be about 10.4 grams. For driver sideapplications, the desired/required amount of propellant grains 90 may beabout 5 grams and for a side inflator application approximately 1.5grams.

The above-identified reduction in the amount of gun-type propellant incomparison to the above-identified FN 1061-10 propellant composition maybe also expressed as a ratio of the weight of the pressurized medium 36to the total weight of propellant grains 90. With regard to the FN1061-10 propellant, the assignee of this application presently uses aratio of about 7.04 for the weight of argon (i.e., the stored gas andcorresponding with the pressurized medium 36 associated with the presentinvention) to the weight of FN 1061-10 propellant. With regard to theuse of a gun-type propellant, to achieve an inflator with the sameoutput, weight, and size as an inflator with FN 1061-10, the ratio ofthe weight of the pressurized medium 36 to the total weight of thepropellant grains 90 ranges from about 10 to about 20, and morepreferably from about 14 to about 18, and is most preferably greaterthan about 15. As can be appreciated, these ratios may be furtherincreased by use of hotter propellants, which would require even lesspropellant. In this regard, because the output gases of gun-typepropellants are essentially free of hot particulate matter, the inflatorcan produce output gases at a higher temperature than can aparticulate-laden inflator such as current state-of-the-art hybrids.This increase in temperature will allow the inflator to be smaller andlighter still, since the hotter gas is relatively more expansive. Inaddition to the foregoing, generally size and weight reductions of theinflator structure may be achieved when using gun-type propellants. Forinstance, when using even a ratio of 7.04 for gun-type propellants in aninflator, the same output may be achieved as in the case of using thesame ratio of FN 1061-10, but the inflator with the gun-type propellantmay be about 50% lighter and smaller than the inflator using FN 1061-10.The ratio of 7.04 can be used equally well for driver side applicationsand side inflators in the noted manner.

The above-identified reduction in the amount of gun-type propellant incomparison to the above-identified FN 1061-10 propellant composition mayalso be expressed as a ratio of the gram moles of the total gas output(i.e., the combination of the propellant gases and the pressurizedmedium 36) to the total weight of the propellant grains 90. With regardto the FN 1061-10 propellant, the assignee of the application presentlyuses a ratio of about 0.192 gram moles/gram of propellant for the molesof the output gas to the weight of the propellant. In comparison andgenerally in the case of a gun-type propellant for an inflator of thesame output, weight, and size, the ratio of the moles of the output gasto the total weight of the propellant grains 90 ranges from about 0.35gram moles per gram of propellant to about 0.6 gram moles per gram ofpropellant, more preferably from about 0.4 gram moles per gram ofpropellant to about 0.5 gram moles per gram of propellant, and is mostpreferably about 0.5 gram moles per gram of propellant. As noted above,for hybrid inflators using gun-type propellants and even using a ratioof 0,192 gram moles/gram of propellant, the inflator output is the sameas a hybrid inflator using FN 1061-10, but the weight and size of thegun-type propellant hybrid inflator is reduced about 50%.

The use of multiple gases for the pressurized medium 36 allows for theuse of at least a gun-type propellant formulation for the propellantgrains 90. Generally, the pressurized medium 36 is composed of at leastone inert gas and oxygen. Appropriate inert gases include argon,nitrogen, helium, and neon, with argon being preferred. The oxygenportion of the pressurized medium is multi-functional. Initially, thereaction of the oxygen with the gaseous combustion products of thegun-type propellant of the propellant grains 90 provides a source ofheat which contributes to the expansion of the inert gas. This allows atleast in part for a reduction in the amount of propellant which isrequired for the gas generator 82. Moreover, the reaction of the oxygenwith the propellant combustion products also reduces any existingtoxicity levels of the propellant gases to acceptable levels. Forinstance, the oxygen will convert preferably a substantial portion ofexisting carbon monoxide to carbon dioxide (e.g., convert at least about85% of CO to CO₂) and existing hydrogen to water vapor (e.g., convert atleast about 80% of the H₂ to H₂ O), and a substantial portion of theunburned hydrocarbons will be similarly eliminated (e.g., eliminate atleast about 75% of the hydrocarbons). As such, the performance of thegas generator 82 as discussed above is significantly improved. That is,the medium 36 and including the oxygen is drawn into the gas generatorhousing 86 through the inlet nozzle 98 on the end 96 of the housing 86by the pressure differential produced by the flow of the pressurizedmedium 36 by the sidewall of the gas generator housing 86 having thedischarge nozzles 200 thereon. As a result, there is a mixing of themedium 36 with the CO and hydrogen-rich combustion products of the gasgenerant which dramatically improves the overall combustion efficiencyof the gas generant, the mixing of the combustion products of the gasgenerant with the oxygen-rich medium 36, and the burning rate of thepropellant grains 90. Gases are then drawn out of the discharge nozzles200 on the sidewall of the housing 86. The above configuration of thegas generator housing 86 thereby greatly improves upon the performanceof the inflator 30 (e.g., by promoting the quick and efficient mixing ofthe oxygen with the propellant gases).

The amount of the at least one inert gas, on a molar basis, is generallybetween about 70% and about 90% and the amount of oxygen, on a molarbasis, is generally between about 10% and about 30% . Generally, it isdesirable to use an amount of oxygen in excess of that based upontheoretical conversions. However, it is also generally desirable to nothave more than about 20% (molar) oxygen in the output gas (i.e., thecombination of the propellant gases and the pressurized medium).

The inflator 30 may be assembled in the following manner. Initially, thegas generator 82 is assembled, such as by: 1) inserting the baffle 100and screen 104 in the gas generator housing 86 adjacent the dischargeend 96; 2) inserting the propellant sleeve 94 in the gas generatorhousing 86; 3) positioning the propellant grains 90 within thepropellant sleeve 94; 4) inserting the baffle 112 and retainer 108 inthe gas generator housing 86 adjacent the end of the propellant sleeve94 opposite the discharge end 96 of the generator; 5) inserting theprimer holder 116, with the ignition/booster material 144 and charge cup148, in the gas generator housing 86; and 6) inserting the actuationguide 140, belleville washer 136, and actuation piston 124 into the gasgenerator housing 86. Thereafter, the various parts are interconnected,such as by welding the gas generator housing 86 to the orifice sleeve74, by welding the diffuser 38 to the boss 66 after positioning theprojectile 50 and initiator 46 in the diffuser 38, welding the closuredisk 70 between the boss 66 and orifice sleeve 74, and welding the boss66 to the inflator housing 34. With the above structure intact, thepressurized medium 36 may be introduced into the inflator housing 34. Inthis regard and in the case of multiple gases, the argon and oxygen maybe separately introduced (e.g., first introduce the argon and/or otherinert gases and then the oxygen or vice versa) into the inflator housing34 through the end plug 42 which is welded to the end of the inflatorhousing 34, or introduced in the pre-mixed state.

The following examples further assist in the description of variousfeatures associated with the use of gun-type propellants in hybridinflators.

EXAMPLE 1

The above-noted HPC-96 propellant was used to form the propellant grains90 having a total weight of 18 grams. Each propellant grain 90 had theconfiguration generally illustrated in FIG. 2, and had a length orthickness of about 0.52 inches, an outer diameter of about 0.29 inches,and a web thickness of about 0.105 inches (one-half of the differencebetween the inner and outer diameters of the propellant grain 90).Moreover, the HPC-96 propellant had the following properties whenignited in the presence of air: an impetus of 363,493 ft-lbs/lb; a heatof explosion of 1,062 calories/gram; a T_(v) of 3490° K.; a molecularweight of the gases of 26.7 grams/mole; a specific heat ratio of 1.2196;and a solid density of 1.65 grams/cubic centimeter. The gas composition,based upon theoretical calculations of normal compositions and assuminga combustion at gun pressures expanded to atmospheric pressure, on amolar percentage basis, was: about 26.5% carbon monoxide; about 19.1%water; about 26.2% carbon dioxide; about 13.7% nitrogen; about 14.2%hydrogen; and about 0.3% other gases.

When the propellant grains 90 of HPC-96 were subjected to the industrystandard Taliani thermal stability test at a temperature of 120° C., thegrains 90 began to discolor within about 40 minutes and ignited withinabout 5 hours. This reduces the desirability of using the HPC-96propellant for the propellant grains 90 since one current industrystandard requires that a propellant for an inflatable safety system doesnot degrade substantially when exposed to a temperature of 107° C. for aperiod of 400 hours, and that the propellant thereafter ignite whenexposed to its autoignition temperature. However, the HPC-96 propellantdoes illustrate certain principles of the present invention and is thusincluded herein.

With regard to HPC-96 propellant grains 90, about 169 grams of thepressurized medium 36 was provided to the inflator housing 34 andconsisted, on a molar percentage basis, of about 5% oxygen and about 95%argon. The inflator 30 had four orifice ports 78 on the orifice sleeve74 with each having a diameter of about 0.266", and the gas generatornozzle 98 had a diameter of about 0.469". No discharge nozzles 200 wereprovided on the sidewall of the gas generator housing 86. As such, nopressurized medium 36 was drawn into the gas generator 82 duringoperation and all discharge was through the nozzle 98.

The pressure variation within the inflator housing 34 during operationof the inflator 30 was similar to that presented in FIG. 3, and thepressure within a 100 liter tank fluidly interconnected with theinflator 30 was similar to that illustrated in FIG. 4 and is generallyrepresentative of the pressure buildup within the air/safety bag 18. Thegaseous output from the inflator 30 included, on a weight percentagebasis, about 1.2% carbon monoxide, about 1.5% carbon dioxide, greaterthan about 2% hydrogen, and about 60 ppm of NO_(x). Consequently, theuse of argon and oxygen in the noted proportions significantly reducedthe amount of carbon monoxide and hydrogen when compared to thetheoretical gaseous output of the HPC-96 propellant noted above. In thisexample, the radial holes were not used, and only a single gas generatoroutlet was used.

EXAMPLE 2

The procedure of Example 1 was repeated but 10.4 grams of HPC-96propellant was used for the grains 90 and about 164.4 grams of apressurized medium 36 was used with the composition being, on a molarpercentage basis, about 15% oxygen and about 85% argon. The performancecurves for the inflator 30 when actuated with these propellant grains 90are illustrated in FIGS. 3 and 4 and the inflator 30 was configured inthe manner discussed in Example 1. Moreover, the gaseous output from theinflator 30 included, on a molar percentage basis, about 2.4% carbondioxide, about 1000 ppm carbon monoxide, about 70 ppm NO_(x), about 38ppm NO₂, and about 0 ppm of hydrogen. Consequently, with the increase inthe amount of oxygen to 15% from the 5% of Example 1, the amount ofcarbon monoxide was significantly reduced without an appreciableincrease in NO and NO₂. Moreover, this also allowed for the use ofsignificantly less propellant.

EXAMPLE 3

The procedure of Example 1 was repeated twice using 10.4 grams of HPC 96and 169.0 grams of pressurized medium 36 composed, on a molar percentagebasis, of about 15% oxygen and about 85% argon. The performance curvesfor the inflator 30 were similar to those presented in FIGS. 3-4 and theinflator 30 was configured in the manner discussed in Example 1.Moreover, the gaseous output from the inflator 30 included about 1000ppm and 800 ppm carbon monoxide, respectively, about 1.0% and 1.2%carbon dioxide, respectively, about 60 ppm and 50 ppm NO_(x),respectively, and about 23 ppm and 20 ppm NO₂, respectively.Consequently, the increase in the amount of oxygen to 15% and thereduction of the amount of HPC 96 reduced the amount of carbon monoxidewithout an appreciable effect upon NO and NO₂. Moreover, the increasedamount of oxygen allowed for the use of less propellant.

As noted above, two existing "traditional" gun-type propellants wereinitially considered for this application--conventional double-base gunpropellants and low vulnerability nitramine (LOVA) gun propellants. Withconventional double-base gun propellants, the system performs asexpected, but will not pass industry standards for long-term storage(e.g., 400 hours at 107° C.). With LOVA gun propellants, the systemperformance was determined to be unsatisfactory unless the propellant isburned at a very high pressure (e.g., above 9,000 psi), which addsweight, cost, and complexity to the design. Generally, it is desirablefor operating pressures of no more than about 4,000 psi to be utilizedfor the inflator. Because no existing propellant is satisfactory forthis application under these conditions, a new propellant formulationwas developed which constitutes a new class of propellant--a propellantwhich combines the ballistic properties of double base propellants(ignites and burns well at low pressure) with the storage properties ofnitramine LOVA propellants (performs well after storage at 107° C. for400 hours). This class of propellants as noted is referred to as ahybrid propellant.

Thermally stable gun-type propellants, unlike nitrocellulose-basedpropellants like HPC-96, when used as the formulation for the propellantgrains 90 include a secondary explosive, namely a nitramine (RDX) in thecase of the LOVA propellants. Other appropriate secondary explosiveswhich may be used in the formulation of the propellant grains 90 includeanother nitramine, namely HMX (cyclotetramethylenetetranitramine), aswell as PETN (pentaerythritol tetranitrate) and TAGN (triaminoguanidinenitrate). Table 1 below provides certain combustion properties for theRDX, HMX, and PETN secondary explosives.

                  TABLE 1                                                         ______________________________________                                               FLAME           COMBUSTION                                                    TEMPERATURE (°K.)                                                                      GASES PRODUCED                                         TYPE   (at 3,000 psi)  w/o excess O.sub.2 (mole %)                            ______________________________________                                        RDX    3348            33%        N.sub.2                                                            25%        CO                                                                 23%        H.sub.2 O                                                          9%         H.sub.2                                                            8%         CO.sub.2                                                     remainder others                                             HMX    3340            33%        N.sub.2                                                            25%        CO                                                                 23%        H.sub.2 O                                                          9%         H.sub.2                                                            8%         CO.sub.2                                                     remainder others                                             PETN   3444            19.5%      CO                                                                 17%        N.sub.2                                                            3%         H.sub.2                                                            30%        H.sub.2 O                                                          24%        CO.sub.2                                    ______________________________________                                    

Generally, in order to achieve a desired combination of certainballistic properties and long-term thermal stability (e.g., to attemptto achieve the ballistic characteristics of a double-base propellant andthe long-term aging characteristics or long-term thermal stability of aLOVA propellant), a secondary explosive may be combined with a bindersystem as the formulation for the propellant grains 90 (as noted above"hybrid propellants"). The phrase "binder system", as used herein,refers to one or more compounds added to the propellant which are usefulfor modifying the physical, chemical, and/or ballistic properties of thepropellant. Useful binder systems include those which incorporatepropellant additives selected from the group consisting of binders,plasticizers, stabilizers, opacifiers, and combinations thereof.

Hybrid propellants for the propellant grains 90 in the hybrid inflator30 exhibit good ballistic properties (i.e. burn rate and combustiontemperature at a relatively low operating pressure), and exhibitacceptable long-term stability (e.g., one industry test for assessinglong-term thermal stability being a statistically sufficient number ofsamples withstanding (not igniting) exposure to a temperature of 107° C.for a period of 400 hours). Another test is inflators withstanding,without unacceptable loss of performance, (which is typicallyestablished/specified by the customer), exposures to a temperature of100° C. for 400 hours. More particularly, propellant grains 90 formedfrom a hybrid propellant burn at a combustion temperature ranging fromabout 2,000° K. to about 3,800° K., at a rate ranging of about 0.1inches per second (0.25 cm/sec) to about 1 inch per second (2.5 cm/sec),and at an operating pressure (the pressure within the gas generatorhousing 84) of about 4,000 psi (27.6 MPa) or less. More preferably, thepropellant grains 90 formed from a hybrid propellant burn at acombustion temperature ranging from about 2,000° K. to about 3,800° K.,at a rate ranging from about 0.3 inches per second (0.76 cm/sec) toabout 0.5 inches per second (1.26 cm/sec), and at an operating pressureof about 4,000 psi (27.6 MPa) or less.

In general, the hybrid propellant formulations comprise from about 50 wt% to about 90 wt % of a secondary explosive and from about 10 wt % toabout 50 wt % of a binder system. More typically, these propellantformulations include from about 60 wt % to about 80 wt % of a secondaryexplosive and from about 20 wt % to about 40 wt % of a binder system.Preferably, the propellant formulation includes from about 70 wt % toabout 80 wt % of a particular secondary explosive and from about 20 wt %to about 30 wt % of a binder system. Other additives and unavoidableimpurities can also be present in these propellant compositions inminute amounts (i.e., in amounts less than about 5 wt % of thecomposition).

Typically, a resinous binder will be part of the binder system for ahybrid propellant formulation for the propellant grains 90. Nearly anytype of binder soluble in common solvents (i.e. acetone, lower alcohols,etc.) can be used. However, it is generally desirable that the binder bean active or energetic compound. That is, it is desirable for the binderto be one which is easily combustible at the above-noted desiredcombustion temperatures and operating pressures. Furthermore, when usinga binder in combination with a plasticizer, it is of course desirablethat the binder be compatible with the plasticizer. Typical binderssuitable for use in the propellant compositions include, but are notlimited to, CA (cellulose acetate), CAB (cellulose acetate butyrate, EC(ethyl cellulose), and PVA (polyvinyl acetate). Moreover, GAP (anenergetic glycidyl azide polymer) may be utilized as a binder componentand such burns substantially more vigorously than CA. As such, it may bedesirable to utilize only GAP as the binder with a secondary explosive.However, due to the significant differences in cost currently betweenGAP and CA, a hybrid propellant formulation may include both GAP and CAbinder components.

Plasticizers can also be part of the binder system for the hybridpropellant formulation for the propellant grains 90. As noted, theplasticizer should be compatible with the binder. Moreover, it isgenerally desirable to use a binder system which is extrudable.Furthermore, at least for certain secondary explosives (e.g.,nitramines) it is desirable to use energetic plasticizers, that isplasticizers that are capable of stable combustion within theabove-noted operating temperatures and pressures. Useful energeticplasticizers include, but are not limited to, those selected from thegroup consisting of nitrate ester plasticizers such as TMETN(trimethylolethane trinitrate), BTTN (butanetriol trinitrate), and TEGDN(triethyleneglycol dinitrate) and glycidyl azide plasticizer and othercompounds such as NG (nitroglycerin), and BDNPA/F (bis(2,2-dinitropropyl) acetal/formal).

Stabilizers may also be included in the binder system for the hybridpropellant formulation for the propellant grains 90. For instance,certain binders and/or plasticizers such as the above-noted nitrateester plasticizers will decompose upon exposure to certain temperatures,and may affect ignition of the propellant grains 90 (i.e., upon exposureto certain temperatures the nitrate ester plasticizer will thermallydecompose to the degree where ignition occurs). Consequently,stabilizers may be included in the hybrid propellant formulation whichwill "react" with the thermally decomposing binder and/or plasticizer tomaintain stability (e.g., reduce the potential for premature ignition ofthe propellant) and thereby enhance the long-term stability of thehybrid propellant formulation. For instance, in the case of a nitrateester plasticizer, useful stabilizers for the propellant formulationinclude those which are active materials, yet are nitrate acceptors.Suitable stabilizers include, but are not limited to, ethyl centralite(symdiethyldiphenylurea), DPA (diphenylamine), and resorcinol.

One hybrid propellant formulation which has the desired ballisticproperties and which has provided sufficient indications of suitablelong-term stability include the combination of the nitramine secondaryexplosive RDX (hexahydrotrinitrotriazine) with a binder system includingthe binder CA (cellulose acetate), the plasticizer TMETN(trimethylolethane trinitrate), and the stabilizer EC (ethylcentralite). Generally, this hybrid propellant formulation may compriseat least about 70 wt % RDX, from about 5 wt % to about 15 wt % CA, fromabout 5 wt % to about 15 wt % TMETN, and no more than about 2 wt % EC.These general relative amounts provide the desired ballistic andlong-term aging properties for the hybrid propellant. However, it willbe appreciated that if propellant grains 90 are to be formed byextrusion from this formulation, refinements of the relative amountswithin the noted ranges may be necessary.

Another hybrid propellant formulation which has the desired ballisticproperties and which has provided sufficient indications of suitablelong-term stability includes the nitramine secondary explosive RDX witha binder system including the binders CA and GAP (glycidyl azidepolymer), and a suitable plasticizer (e.g., GAP plasticizer, TMETN, ATECand combinations thereof). Generally, this hybrid propellant formulationmay comprise from at least about 70 wt % and typically between about 70wt % and 80% RDX, from about 5 wt % to about 15 wt % CA, and from about5 wt % to about 15 wt % GAP, and about 5 wt % to 15 wt % plasticizer.These general relative amounts provide the desired ballistic andlong-term aging properties for the hybrid propellant. However, it willbe appreciated that if propellant grains 90 are to be formed byextrusion from this formulation, refinements of the relative amountswithin the noted ranges may be necessary.

In the case of hybrid propellants disclosed herein, as in the case ofthe double-base and LOVA propellants discussed above, during combustionsignificant quantities of carbon monoxide and hydrogen are produced(e.g., 35% CO and 19% H₂). Again, the formation of carbon monoxide andhydrogen gases through combustion of an inflator propellant wouldnormally be unacceptable for an automotive inflatable safety system.However, when these types of hybrid propellants are used in the hybridinflator 30 and as noted above, the pressurized medium 36 includesoxygen such that a substantial portion of the carbon monoxide andhydrogen (e.g., 95% ) are converted during combustion or as part of apost-combustion reaction to harmless carbon dioxide and water vapor. Theuse of stored oxygen gas is particularly desirable because it obviatesthe need to include an oxygen source (e.g., potassium perchlorate) inthe hybrid propellant formulation. Moreover, the highly exothermicreaction between the produced combustion gases of the propellant withthe stored oxygen is particularly desirable because it enhances theheating value of the propellant, thereby minimizing the amount ofpropellant required for expanding the air/safety bag.

The hybrid propellants, when formulated into the propellant grains 90and incorporated into the hybrid inflator 30, may be used in the amountsspecified above with regard to the gun-type propellants and specificallyincluding the particulars presented above with regard to the relativeamounts of propellant grains 90 and pressurized medium 36. Moreover, therelative amounts of oxygen and the one inert gas for the pressurizedmedium 36 may also be used in the case of the hybrid propellantsdisclosed herein.

The following examples further assist in illustrating pertinent featuresof hybrid propellant formulations which include a secondary explosiveand a binder system. As previously noted, all references to "wt %"refers to weight percentage.

EXAMPLE 4

A hybrid propellant composition comprising at least about 70 wt % RDX(hexahydrotrinitrotriazine), from about 5 wt % to about 15 wt % CA(cellulose acetate), from about 5 wt % to about 15 wt % TMETN(trimethylolethane trinitrate) and no more than about 2 wt % ethylcentralite was prepared and formed into cylindrical grains having anaverage density of about 1.7132 g/cc. A 10 g test sample was placed intoa heavywall bomb chamber and fired into a tank. The test sample had acombustion temperature of about 2578° K. and exhibited acceptableballistic properties (i.e., a burn rate of 0.47 inches per second (1.18cm/sec) at 4000 psi (27.6 MPa)). Generally, the performance curvesgenerally approximated those presented in FIGS. 3-4. The gas producedcontained about 36% carbon monoxide, about 24% nitrogen, about 19%hydrogen, about 16% water vapor and about 5% carbon dioxide. Long-termthermal stability of the composition was assessed and determined to beacceptable (e.g., the propellant itself was exposed to a temperature of107° C. for 400 hours and did not ignite; the propellant when containedwithin a hybrid inflator did not ignite when exposed to a temperature of107° C. for 400 hours, and thereafter upon activation of the same, theperformance of the inflator was substantially unaffected by the heattreatment).

EXAMPLE 5

A propellant composition comprising at least about 70 wt % RDX(hexahydrotrinitrotriazine), from about 5 wt % to about 15 wt %cellulose acetate, and from about 5 wt % to about 15 wt % GAP (glycidylazide polymer) was prepared and formed into cylindrical grains having anaverage density of about 1.6857 g/cc. A 10 g test sample was placed intoa heavywall bomb chamber and fired into a tank. The test sample had acombustion temperature of about 2,357° K. and exhibited acceptableballistic properties (i.e., a burn rate of 0.48 inches per second (1.18cm/sec) at 4,000 psi (27.6 MPa)). Generally, the performance curvesgenerally approximated those presented in FIGS. 3-4. The exhaust gasproduced contained about 37% carbon monoxide, about 25% hydrogen, about25% nitrogen, about 10% water vapor and about 3% carbon dioxide. Longterm thermal stability of the composition was assessed and determined tobe acceptable (e.g., the propellant itself was exposed to a temperatureof 107° C. for 400 hours and did not ignite; the propellant whencontained within a hybrid inflator did not ignite when exposed to atemperature of 107° C. for 400 hours, and thereafter upon activation ofthe same, the performance of the inflator was substantially unaffectedby the heat treatment).

The foregoing description of the invention has been presented forpurposes of illustration and description. Furthermore, the descriptionis not intended to limit the invention to the form disclosed herein.Consequently, variations and modifications commensurate with the aboveteachings, and the skill or knowledge of the relevant art, are withinthe scope of the present invention. The embodiments describedhereinabove are further intended to explain best modes known ofpracticing the invention and to enable others skilled in the art toutilize the invention in such, or other, embodiments and with thevarious modifications required by the particular applications or uses ofthe invention. It is intended that the appended claims be construed toinclude alternative embodiments to the extent permitted by the priorart.

What is claimed is:
 1. An inflator for an inflatable safety system,comprising:an inflator housing; a pressurized medium contained within atleast said inflator housing, wherein said pressurized medium consistsessentially of at least one inert gas and oxygen and wherein saidpressurized medium is the only pressurized fluid contained within saidinflator prior to any activation of said inflator; a gas generatorinterconnected with said inflator housing and comprising a gas generatorhousing and at least one gas generator outlet: a propellant containedwithin said gas generator housing comprising a secondary explosive and abinder system, wherein said propellant has a burn rate ranging fromabout 0.1 inches per second (0.25 cm/sec) to about 1 inch per second(5.0 cm/sec) at 4,000 psi (27.6 MPa), a combustion temperature rangingfrom about 2,000° K. to about 3,800° K., and has lone-term thermalstability, said secondary explosive being selected from the groupconsisting of RDX (hexahydrotrinitrotriazine), HMX(cyclotetramethylenetetra-nitramine) , PETN (pentaerythritoltetranitrate) , and TACN (triaminoguanidine nitrate), said binder systembeing selected from the group consisting of polymeric binders,plasticizers, stabilizers and combinations thereof, said binder systemcomprising at least one of an energetic glycidyl azide polymer, anitrate ester plasticizer, a glycidyl azide plasticizer, nitroglycerin,and BDNPA/F (bis (2,2-dinitropropyl) acetal/formal); and an inflatoractivation assembly comprising an ignitable material other than saidpropellant, wherein said pressurized medium is released from saidinflator housing and said propellant is ingnited upon initiating saidinflator activation assembly.
 2. An inflator, as claimed in claim 1,wherein: said at least one inert gas is argon.
 3. An inflator, asclaimed in claim 1, wherein:said pressurized medium, on a molar basis,is about 70% to about 90% of said at least one inert gas and from about10% to about 30% of said oxygen.
 4. An inflator, as claimed in claim 1,wherein:said pressurized medium, on a molar basis, is about 85% of saidat least one inert gas and about 15% of said oxygen.
 5. An inflator, asclaimed in claim 1, wherein:propellant gases from combustion of saidpropellant and said pressurized medium are mixed to define an outputgas, said output gas containing, on a molar basis, no more than about25% oxygen.
 6. An inflator, as claimed in claim 1, wherein:saidsecondary explosive comprises from about 50 wt % to about 90 wt % ofsaid propellant and said binder system comprises from about 10 wt % toabout 50 wt % of said propellant.
 7. An inflator, as claimed in claim 1,wherein:said secondary explosive comprises from about 60 wt % to about80 wt % of said propellant and said binder system comprises from about20 wt % to about 40 wt % of said propellant.
 8. An inflator, as claimedin claim 1, wherein:said secondary explosive comprises from about 70 wt% to about 80 wt % of said propellant and said binder system comprisesfrom about 20 wt % to about 30 wt % of said propellant.
 9. An inflator,as claimed in claim 1, wherein:said secondary explosive comprises RDX(hexahydrotrinitrotriazine) and wherein said binder system comprisescellulose acetate, TMETN (trimethylolethane trinitrate) and ethylcentralite.
 10. An inflator, as claimed in claim 9, comprising:at leastabout 70 wt % of said RDX (hexahydrotrinitrotriazine), from about 5 wt %to about 15 wt % of said cellulose acetate, from about 5 wt % to about15 wt % of said TMETN (trimethylolethane trinitrate), and no more thanabout 2 wt % of said ethyl centralite.
 11. An inflator, as claimed inclaim 1, wherein:said secondary explosive comprises RDX(hexahydrotrinitrotriazine) and said binder system comprises GAP(glycidyl azide polymer) and a plasticizer.
 12. An inflator, as claimedin claim 1, wherein:said secondary explosive comprises RDX(hexahydrotrinitrotriazine) and said binder system comprises celluloseacetate and GAP (glycidyl azide polymer) and a plasticizer.
 13. Aninflator, as claimed in claim 12, comprising:at least about 70 wt % ofsaid RDX (hexahydrotrinitrotriazine), from about 5 wt % to about 15 wt %of said cellulose acetate, and from about 5 wt % to about 15 wt % ofsaid GAP (glycidyl azide polymer), and from about 5 wt % to about 15 wt% of a plasticizer selected from the group consisting of ATEC (acetyltriethyl citrate) and GAP plasticizer.
 14. An inflator for an automotiveinflatable safety system, comprising:an inflator housing; a pressurizedmedium contained within said inflator housing; a gas generatorinterconnected with said inflator housing and comprising a gas generatorhousing and at least one gas generator outlet; a propellant containedwithin said gas generator housing, said propellant comprising asecondary explosive and a binder system, wherein said secondaryexplosive comprises RDX (hexahydrotrinitrotriazine) and wherein saidbinder system comprises cellulose acetate, TMETN (trimethylolethanetrinitrate) and ethyl centralite; and an inflator activation assembly,wherein said pressurized medium is released from said inflator housingand said propellant is ignited upon initiating said inflator activationassembly.
 15. An inflator, as claimed in claim 14, comprising:at leastabout 70 wt % of said RDX (hexahydrotrinitrotriazine), from about 5 wt %to about 15 wt % of said cellulose acetate, from about 5 wt % to about15 wt % of said TMETN (trimethylolethane trinitrate), and no more thanabout 2 wt % of said ethyl centralite.
 16. An inflator for an automotiveinflatable safety system, comprising:an inflator housing; a pressurizedmedium contained within said inflator housing; a gas generatorinterconnected with said inflator housing and comprising a gas generatorhousing and at least one gas generator outlet; a propellant containedwithin said gas generator housing, said propellant comprising asecondary explosive and a binder system, wherein said secondaryexplosive comprises RDX (hexahydrotrinitrotriazine) and said bindersystem comprises GAP (glycidyl azide polymer) and a plasticizer; and aninflator activation assembly, wherein said pressurized medium isreleased from said inflator housing and said propellant is ignited uponinitiating said inflator activation assembly.
 17. An inflator for anautomotive inflatable safety system, comprising:an inflator housing; apressurized medium contained within said inflator housing; a gasgenerator interconnected with said inflator housing and comprising a gasgenerator housing and at least one gas generator outlet; a propellantcontained within said gas generator housing, said propellant comprisinga secondary explosive and a binder system, wherein said secondaryexplosive comprises RDX (hexahydrotrinitrotriazine) and said bindersystem comprises cellulose acetate and GAP (glycidyl azide polymer) anda plasticizer; and an inflator activation assembly, wherein saidpressurized medium is released from said inflator housing and saidpropellant is ignited upon initiating said inflator activation assembly.18. An inflator, as claimed in claim 12, comprising:at least about 70 wt% of said RDX (hexahydrotrinitrotriazine), from about 5 wt % to about 15wt % of said cellulose acetate, and from about 5 wt % to about 15 wt %of said GAP (glycidyl azide polymer), and from about 5 wt % to about 15wt % of a plasticizer selected from the group consisting of ATEC (acetyltriethyl citrate) and GAP plasticizer.